Water policy after the flood

There’s already some finger-pointing about the management of Brisbane’s dams in the weeks leading up to the flood. I don’t want to deal with that while the emergency continues, but I will make a couple of suggestions regarding future policy in Brisbane and elsewhere

* The historical statistics on the frequency of severe rainfall events (both droughts and floods) have proved to be of little value. Everywhere in Australia, we need to work on the assumption that extreme events will be more common in the future than they were in the (pre-2000) past.[1]

* As regards Wivenhoe Dam, we need a much more cautious approach to flood mitigation, going into wet seasons with a substantially larger reserve capacity. This in turn will reduce Wivenhoe’s usefulness as a water supply source, and buffer against drought.

* One response that is immediately available to us is to turn on the water recycling plant, built at great expense during the drought and never used. Current policy is to turn it on when average dam levels are at 40 per cent. This trigger should be raised significantly. As a very rough guide, it appears that when our dams are at 100 per cent of normal we currently have enough storage for four years supply. If instead we cut the maximum to three years supply (75 per cent0, we could (roughly) cancel the impact on supply by turning on the recycling plant at 65 per cent (40+25)

On a personal note, I’ve had some reports from home and it appears that cleanup will go faster than expected and that our biggest loss (the car) is covered by insurance.

Many others are not so lucky. And, as was discussed in comments to the previous thread, floods in poor countries regularly cause many deaths (400 in Brazil and 40 in the Phillipines in the time I’ve been following our own flood) and wipe out the few possessions of very poor people. If you are giving to flood relief appeals for Queensland (as I hope you are), please think about also sparing a few dollars for emergency relief or long-term development aid for the truly poor.

Update It’s been argued pretty convincingly in comments here and elsewhere that the additional mitigation capacity in the estimates above would only have had a marginal influence on the current floods, given the volume of rain that fell. Still, I think the basic premise is right. We will need more mitigation capacity and that means less water at higher cost.

Another point I meant to make earlire is that more reliable forecasts of El Nino and La Nina events would be of great value in managing water supply in a highly variable environment.

fn1. I will have a lot more to say about human-caused climate change in the near future. But until I’ve had my say, I request everyone to avoid any discussion of the AGW topic in this thread – failure to heed this warning will lead to deletion and may result in a permanent ban. Feel free to continue discussion in the agnotology thread.

The question then has to be JQ, how much effect on flooding will 25% of Wivenhoe’s capacity have on flood levels? It is now going to take at least 10 years before we know if all previous climate cycles are null. Will drought return?, or are we now into a new shorter climate pattern.

The real problem is that this whole subject of water retention or release is guaranteed turmoil in a conflictual political environment. Every choice has a downside and that downside is fuel for political attack. I think that there is going to be a huge need for an independent national water management authority (may already exist) to exercise water planning on the basis of best science.

for our current flood it would not be too hard to calculate how much better things would have been with another 25% capacity in Wivenhoe. It would have helped, but not as much as one might think. Firstly the water coming from the Bremer river and Lockyer valley enters the Brisbane river downstream from the Wivenhoe dam. That was a lot of water. Secondly the Wivenhoe catchment was delivering huge inflows – around a half total capacity per day! (as against 25% = 1/8th total capacity using the measurement system of seqwater).
So it would help, but not much – the dam operators would still have had to release an enormous amount from Wivenhoe.
It seems that the rain stopping allowed the dam operators to cut the Wivenhoe outflows as the water from the Bremer and Lockyer came into the Brisbane river. Good planning and understanding of the specific system combined with luck to prevent an even greater disaster.

It seems to me that the Brisbane-valley flood was well prepared for and managed. The risks to utilities, disease and the need for information and evacuation all appear to have worked well. This is taxes at work.

Is it the case that no property was damaged that was not on a well known flood plain.

The real issues are the forces that allowed development on a flood plain.

So far it appears that elsewhere in Australia only flood plains are flooding and levees are doing their jobs.

However what happened in Toowoomba is a different issue and we need a formal Inquiry here. Did the City Council or Shire administrations have previous knowledge of the potential waterflows through various creek flats in local valley situations? What is the flood history of this region?

If they can move townships when constructing the Snowy Mountains scheme in the 1950′s they can easily move town centres off floodplains now.

Unlike earthquakes and bushfires which jump containment lines, floods on floodplains should cause no untoward or heart-wrenching damage.

Australia needs droughts and floods and you cannot over-rule nature just because some business wants to locate on a cheap bit of land, or local authority desires to skimp on bridge and earthworks costs. I would image, that away from water-front prestige, average householders on flood plains have been forced to live on cheaper sites because their incomes from work are insufficient for them to purchase a decent life.

Chris Warren is right on the money. “The real issues are the forces that allowed development on a flood plain…” or more precisely on “flood plains” plural.

In another post, I called for the progressive movement of all towns and suburbs above the 1 in 100 years flood levels. Along with this, there should be a ban on all future development below such flood levels. As Prof JQ noted, climate variability and climate change render historically determined probabilities somewhat problematic. However, the 1 in 100 level would be a good starting benchmark.

Assistance for these moves should come from the state and the state should progressively buy such land and houses at market price. The land should be returned to use as parks, natural riparian buffer, wilderness and/or grazing as appropriate on a region by region basis.

Selling out of a flood prone area should be voluntary but those who remain would be required to take certain further measures (too long winded to define here).

Where key infrastructure, like the Rocklea markets and industrial area, exist in a flood prone area, we need case studies which cost moving the infrastructure and compare that to implementing full levee protection and a raised road and rail link to a secure high-ground transport hub.

I am sure, in the long run, prevention is more economic than widespread flood recovery. Of course, there would be a level of measures beyond which we would run into the issue of negative returns. We need to examine these issues fully.

It may be that the local authorities in Toowoomba failed in some way. It may also be that the decades-old obsession with cutting spending no matter what is bearing some fairly nasty fruit. An inquiry is an excellent idea.

The Toowoomba and Grantham flash floods opened all our eyes to the power of flash flooding. Local flash floods of this magnitude in Australia have been very rare to date. They may become more common now with AGW. It’s hard to fault anybody for not predicting these flash floods. Now we have seen them in this area we may need to look at a few new issues.

Toowoomba may need some expensive new floodways which will only be fully utilised once every 50 years. The Grantham issue is maybe even more complex to address in prevention terms.

Playing politics with such events seems to be reserved for the likes of Barnaby Joyce, instantly last week into the “what we need are dams, dams, and more dams” routine. Just as with the call for ever more prescribed burning after every bushfire, the people who want to do things that will cause environmental damage seem to have free pass to politicise such events, everyone else should shut up or be accused of playing politics.

I agree, of course (again as with bushfires) that there needs to be a lot more emphasis on both city/suburban planning, and on building codes, in flood prone area, but I am willing to bet to my last dollar (not, I’m afraid, a huge amount) that calls for regulation will be poo poed by housing industry people, radio shock jocks, and right wing politicians generally, and quietly shelved.

I would also like to see some enquiry into ecological methods of flood control – eg the use of wetlands, reed beds, riverbank and hill slope vegetation – but I am betting (second last dollar) that land clearing and draining practices will continue unabated.

We could hire Delta Works, the Dutch project started after the same storms that inspired the Thames Barrier. Among the most impressive things about the Dutch approach is that it is very long term. The project began in 1953 and was completed in 2010. They also take science seriously. Within days of Katrina they had named a new commission to investigate the impact of sea level rises. The commission proposed a new project that will take 190 years to complete. The US sought (and of course ignored) their advice after Katrina. Why do serious policy when you can chant ‘Drill baby, drill’.

I believe that developers have resorted to the courts to overturn council and government vetoes on developing unsuitable land. That should also be added to a review list, I think.

However, given the current climate of develop at all costs and the floods are the Greens’/Peter Garrett’s fault, I fear it’ll be business as usual. I hope I am proved wrong, but like you, I think my last couple of bucks will remain safely in my purse.

It would be expected that the review that will take place after the event(s) will look closely at the strategies for dam management and related issues.

Another matter that will hopefully get attention is who pays and how to pay for repairing all the damage. At the moment once a threshold has been reached, the cost to the Queensland Government is shared by all States and the Federal governments under a cost-sharing agreement.

Because the costs in this case are well above the threshold, this means Queensland Government’s costs for these floods will be shared by all Australians and not just Queenslanders. I’m not sure of the details of what is covered under the cost-sharing arrangements but it wouldn’t include individual losses.

It’s past time to look at different ways of addressing the matter of floods and other disasters across the board. Eg funding of volunteer emergency services, more equitable reimbursement for individual property damage (insured vs uninsured etc), urban and rural planning, adaptation, how to more quickly address the root causes etc etc.

The Victorian Bushfire Royal Commission made some good recommendations (and some very bad ones), but it didn’t address all these issues and for some of those it did address, it didn’t do so adequately. The review of this disaster will provide an opportunity to do it better.

It’s not possible to prevent all disasters. For example, the Lockyer Valley incident was a freak event and probably the majority of contributors to Queensland’s economy was affected by this summer’s floods.

I agree that all efforts should be made to dissuade people from building in flood prone areas, or to better flood-proof buildings on flood plains. Given that much of Queensland’s most productive lands are flood plains – as is much of the most productive land in other states – to stop anyone from living on or using flood plains for agriculture and towns that provide the requisite services would severely reduce the productive capacity of Australia.

Any changes to existing arrangements for response, relief and recovery need to take as a given that much of Australia is prone to drought, fire and flood. The focus has to be on how to best protect major centres against such events, ensure there are adequate resources to respond to multiple simultaneous widely dispersed large events (including volunteer services), ensure there are funds to pay for the cost of response and recovery, and address the root cause of the increasing frequency and severity of these events.

Some communities on the upper Mississippi floodplain in the USA either dissolved or simply moved to high ground. It is not sustainable to maintain communities that will experience hundreds of millions of dollars every year or so, or even every decade. It will be interesting to see whether the Australian goverment has the mindset of a petit bourgeois or if it will have the courage to do think big.

IMO, the response coordinated by the Queensland Government to the floods this summer sets a new benchmark in Australia (and probably internationally) for emergency response. It has been most impressive.

Our problems in Australia, along the eastern seaboard right down to South Australian Murray mouth, start with multi-year wets after serious drought. The largest drought breakers have been strong – as in consistent – la Nina stretches immediately following prolonged drought. The la Nina phenomena is in itself only a necessary condition, not sufficient. Although there are only a handful of serious flood events for which a decent record is available – more recent ones possessing much more data of course – it seems that a serious flood requires a one-two punch, a combination of a decent la Nina surviving across one season to spill into another, and something else, like a series of unusual summer rain events in Victoria. These may occur through meteorological structures, such as blocking highs. Anyway, the signature event of the 1956 floods along Mannum and other river towns was such a combination. Not only the Murray, but other river systems filled beyond capacity. “Normally”, river systems far apart won’t fill together, but weather being what it is…

And then there is the encroachment of humans into every good part of the environment, bit by bit. Once high ground is taken, the next band of undeveloped low ground becomes the new high ground – until the flood plains are all that is left. Murray Bridge at Sturt Reserve has a fabulous juxtoposition of this phenomenon. Perhaps 100–150 metres away from the current river’s edge are a series of multi-storey houses on high ground, with a wonderful view of the river extent. Some years later the deal was done, and the flood plain immediately beneath these houses has been developed, with clearly unprotected virgin homes. Flamin’ heck! I don’t want to have a go at anyone who wants to buy into such houses, but please be sure to have really thought about it. Just because someone was willing to take a risk developing that area is not reason enough to take a more enduring stake in the outcome by buying a home. Developers build houses, not homes. They have an entirely different view on the nature of risk.

Could the Murray Bridge council provide some clear reasons why they risked the placing of new houses so close to the river’s edge – ironically a few tens of metres from the tourist display, a post with the historical floods marked on it; the 1956 flood is the only one requiring raised eyes – and should they eventually flood again, what words they’ll use to placate the angry (ex-) residents? Maybe I’ll attend the next council meeting…

The 1956 floods around my location are a case in point. It isn’t good enough to plan again “for a 1956 flood”, or “for a 1974 flood”, or whatever. The point is to decide upon how to

I keep hearing this “flood plain” business being bandied about by people who obviously don’t know much at all about Brisbane’s geography. Its only really straight-out flood plain is around Rocklea, Oxley and the river mouth where Tingalpa and the airport are. Lots of this area is light or heavy industrial as is typical of any Australian city (the Marrickville area, anyone?). The river winds its way among hilly country. The rest of Brisbane, including the hardest hit areas like Milton and Indooroopilly, is actually built into riverine hills. Brisbane is HILLY like Sydney east of Parramatta, not flat and featureless like most of Melbourne.

When it floods the river backs up the creek beds and the former creek beds up streets and floods these. This is why some houses go totally under and the next street is untouched. The pattern of this flooding is known, sure, but many of these areas are also Brisbane’s OLDEST areas, much of it is pre-1946 housing stock along with more modern development (duplexes, townhouses) on subdivisions of the existing bigger blocks.

Sometimes in big storms we get the opposite problem (like Toowoomba). The water rushes down the gullies to the creek beds and river beyond. A lot of the drainage system is built to withstand this issue, not the opposite one (the river coming back up the stormwater flows).

Dr Vervort mentions the two methods of catchment management. “preventing floods by focusing on land management, increasing infiltration and slowing down the water before it reaches the stream” and “the second part of the risk equation, reducing damage rather than occurrence. A key element of this type of management involves *limiting development* on flood plains to allow the river to run freely.”

Obviously the powers that be have failed to use these catchment management strategies, except perhaps for interpreting the “slowing down water before it reaches the stream” as whacking a dirty great dam in somewhere. This has been of value only in less than major floods.

I think the dam – Wivenhoe – did have value, and we need water storage anyway. But clearly the idea that the only way to manage living in an environment is through massive physical and technological intervention is deeply flawed.
Unless of course your primary goal is to make money within your own lifetime.

Just about any problem Australia faces has population growth mixed up in it somewhere (more often than not as a root cause) and this issue is no different; a rapidly expanding city and settlement in flood prone areas plus stretched water resources. Until governments of all persuasions govern for the majority rather than vested interests and short term political horizons the severe problems caused by unecessary population growth can be expected in all manner of areas.

This is not to minimize the disaster or problems from not being careful where you build, but some infrastructure really does want to be at river-edge or sea-level.

For seal level rise, her’s a map centered on Brisbane. Run the SLR up and down, make your own planning estimate of SLR for 2100 and 2200AD, unfortunately limited to integer #s. Just as a guess try 1-2m and 4-6m.

Note: dikes against storm surge and against SLR are different. For the latter, if you are below sea level, and it rains, you have to pump the water up.

@Chris O’Neill
It is too early to make the strong claim you link to. The data given at those links is inadequate – no levels for Sat/Sun and no info on what was happening in the catchment – which definitely was not steady rain. Without that info, and the legislative framework under which SEQ Water operates criticisms are very speculative.

Massive populations = massive physical and technological intervention
Massive population is the path humanity has chosen and is choosing. Having a massive population is clearly more important to humanity than avoiding the problems it causes and will cause.

The massive physical and technological developments occurred in the industrial revolution when population was much smaller.

Humanity has not chosen massive population, this is an unplanned consequence of other activity. When it gets to the stage where extra population costs too much, humanity can, does, and should choose otherwise.

The world has less need now for “massive physical and technological developments” than the glaring need for a better distribution of the current level of development. This sharing is best facilitated in the absence of population pressures.

Irony Alert On. It is always easier to manage a complex evolving situation with the benefit of hindsight. Irony Alert Off.

I concur with gregh. A lot of data and hydrological expertise in interpreting that data would be required to assess the management of Wivenhoe levels during the last month. I suspect SEQ Water would run river flow and height modelling programs continually as an aid to managing releases. The entire Brisbane-Bremer system and catchment rain events over time is a complex entity to model and make predictions for in hydrological terms.

By all means, do a considered post-event review. However, I doubt that an alarmist journalist’s back of the envelope assessment amounts to anything.

@Ikonoclast
From the interviews I heard on the radio – until we lost power – I was very impressed with the various people involved in trying to manage the flood.
It struck me that politics (broadly construed) was taken out of the management as the situation developed so quickly and was of such a scale that people who knew what they were doing were acting without a great deal of external interference.

Pointing fingers makes sense where foresight into likely consequences, upon taking certain actions, is available. Not much sense in it when an event ultimately comes down to luck of the draw, eg available meteorological forecasts and juggling of controlled dam releases. Imagine the uproar if a flood event was caused by releasing so much water that a downstream storm combined to flood out some houses somewhere? But then, holding onto the dam release for just one more day, hoping storms are going to fade before the dam is full?

On the contrary I think people in this line of work deserve a round of applause. Governments both state and federal, on the other hand…probably need to consider how new towns and cities are planned for, and may be encouraged to develop away from the high risk areas. Oh, our manufacturing jobs went off-shore, you say? Bum, it will be hard to build a new town if there is no reason to settle there
At the least though, town planners should be subject to jeers for allowing/encouraging development along the big Murray. Leave that ground for parks and the like, or even farming, but keep the houses off.

First, I am sorry if this offends your ban on AGW, but I do not know what that is: anthropogenic global warming, anti global warming, accelerated global warming? It’s probably not the on line magazine A Girls World.
I disagree with your 1st dot point on two grounds. Rainfall in not increased over all of Australia – the southern half of WA has considerably less rain than it had 40 years ago, with the decrease said to have started around 1971. Second the history is important. As I mention in my admittedly not widely read blog, La Nina is not enough to explain the current summer Australian rain pattern. And parts of Queensland have had floods for longer than we have recorded their history.
It may be that better use of current and perhaps future dams will decrease the severity of future floods. But, “It may be” is not good enough. We need a non-political scientific study of past, present and future rainfall and weather patterns as part of the beginning of a flood mitigation study. The outcome might be more dams, but it could also be water directing channels or even suggesting that some parts of Queensland should not be sites for permanent housing.
Regrettably, the study is required soonest, despite the obvious urgency of attending to the personal and public tragedies that these floods have caused. Rebuilding a house so that it can be flooded next year still without insurance is not the best long term way to handle tragedy.

@David Horton
Of course, the big winners to date have been property developers, who build in areas that should be excluded from development. They construct their buildings, sell them on and walk away, carrying none of the risk.

Regulation hasn’t been working too well (developer donations at risk?). Perhaps the likes of Nearmap will help people make an informed property purchase. As an alternative to regulating the construction, I wonder how feasible it might be to make it a condition of the land title that flood insurance be maintained for any building on the site?

my understanding is that the self actuating uncontrolled release of water at the Wivenhoe dam did not occur and has bugger all to do with staffing levels.

The self actuating uncontrolled release of water occurs at maximum dam level to protect the dam. This has nothing directly to do with releases to preserve flood mitigation capacity which are supposed to begin when the level exceeds 100% of water supply capacity. These releases are manually controlled, as far as I know.

@Chris Warren
To amplify a little. The South WA decrease rainfall pattern has persisted for 40 yrs and has occurred with La Nina and El Nino and neither. Furthermore there is no logical reason to suppose that the weather there should be affected by La Nina cycles. The cold fronts are simply passing further south and so there is less rainfall over the land. The 1974 and the current Qld floods can be associated with La Nina. However there have been floods with no La Nina and there have been La Nina events with no floods. An explanation in addition to La Nina is thus required to explain flooding and certainly to predict it.

It is too early to make the strong claim you link to. The data given at those links is inadequate – no levels for Sat/Sun

I like the irony, “no levels for Sat/Sun”. This wouldn’t have anything to do with them not working and managing the dam release on Sat/Sun, would it? That was the whole point, they set the release rate on Friday, went home for the week-end, came in on Monday morning and thought “Oh sh!t”.

@Chris O’Neill
one of the issues they were concerned about was the triggering of the auto-release, which apparently would limit their ability to control release for mitigation. The chap I heard speaking about this at the time was actually more than ‘concerned’

Imagine the uproar if a flood event was caused by releasing so much water that a downstream storm combined to flood out some houses somewhere?

They could have released a lot of water without even causing a minor flood level in Brisbane. The guage at Jindaleee was below minor flood level until 1 pm on Tuesday the 11th and below moderate flood level until 7 pm. So they could have had higher releases at Wivenhoe right through the weekend until midday on Monday the 10th without causing any more than minor flooding on the Brisbane River in Brisbane. Of course, if you’re not thinking about these issues until after 9 am on Monday morning then you’re probably already in deep doo-doo and there’s very little you can do about it. If they really did set-and-forget the dam release for the whole weekend then they are guilty of massive negligence.

Given the inflows (said to be in the range of 1.15-1.6PL per day i.e. about 4-5 times the outflow they were running and roughly 40-60% of total dry capacity) it’s hard to imagine that even a totally empty Wivenhoe would have made much difference. There were massive flows down the Bremer as well which would have been unaffected.

I wasn’t aware that working at the week-ends requires great and incredibly impressive hindsight. I guess I should be thankful you didn’t still write something that shows you didn’t understand the auto-trigger is not directly related to flood mitigation release.

Given the inflows (said to be in the range of 1.15-1.6PL per day i.e. about 4-5 times the outflow they were running and roughly 40-60% of total dry capacity) it’s hard to imagine that even a totally empty Wivenhoe would have made much difference.

Is that a “small wrong makes a right” argument? In any case taking two days out of the flood flow would have made a big difference.

Chris O’Neill, so as to put many of your concerns at rest on the 14 January 2011 the Premier said ‘The Wivenhoe dam will continue to see managed and controlled releases … at the rate of three and a half thousand cubic metres per second…over the next five or six days ….(before next Friday’s king tide and…all throughout that release it is being carefully calculated so that the release, the maximum height of the water during that release will stay within the banks of the river system’.

Careless of me to say “back at work” because I have no idea if they even left work.

Some of these rainfalls on top of a wet catchment are extraordinary. It is certainly worth a look at dam operations but to put any sort of blame for the floods on them is wrong. As has been said upthread, had the dams been completely empty there would still be major flood damage.

Fine tuning the operations of the Wivenhoe will help a little for major flood mitigation. Re-forestation, restoring wetlands, reducing population and development, will have the best mitigation effects.

the authorities had to decide what amount of water must be released in line with the expected high tide and as far as I know they correctly controlled the volume of water

So holding back water when it would have only produced minor flooding and then releasing it when it goes on to aggravate major flooding is correctly controlling the volume of water? You must have a different meaning for the word “correct” than the one I’m familiar with.

The fact is that SEQ Water let Wivenhoe go to 148.4% and Somerset to 154.7% during a period when marginal additional releases would not even have produced minor flooding in Brisbane, let alone moderate flooding. They have a case to answer.

No that doesn’t put any of my concerns at rest. It doesn’t answer the question of whether they were managing the release at the weekend before the flood and it doesn’t answer the question of why they allowed Wivenhoe go to 148.4% and Somerset to 154.7% during a period when marginal additional releases would not even have produced minor flooding in Brisbane, let alone moderate flooding.

Chris O’Neill, Isn’t that human nature? Live in hope? How could they know it was going to get so bad? This is the problem with relying on such structures for flood mitigation. Better to live within nature’s extremes than try and control the extremes.

gregh, settle down, everyone’s entitled to get a bit emotional here from time to time and it doesn’t detract from your overall contribution.

As has been said upthread, had the dams been completely empty there would still be major flood damage.

For a start, you’re ignoring the concept of quantity in this statement. Less flood means less damage, even if you still call less damage “major”. Also, 1 metre lower would have been a lot less damage (it would have been below major flood level) and if they had kept Wivenhoe and Somerset to 100% until midday Monday the 10th then I’d like to know if that could have taken 1 metre off with that reserve.

Fine tuning the operations of the Wivenhoe will help a little for major flood mitigation. Re-forestation, restoring wetlands, reducing population

Reducing population? Not in our lifetimes.

Isn’t that human nature? Live in hope? How could they know it was going to get so bad?

That’s beside the point. They’re not supposed to assume it won’t be bad, i.e. policy is to keep it at 100% unless they have a very good reason for letting it go higher. Without a very good reason, and I have yet to see one, they were violating policy.

When Chris O’Neill finishes correcting the SEQ hydrologists in flood management, he will be performing brain surgeries at Royal Brisbane and then flying to Florida to perfect NASA’s next space project.

Don’t be so hard on yourself. You lost the plot in one comment. Many of us have done that. Get that one comment deleted. You are a good contributor overall. Try humour as I have done above. Although that might get deleted too.

I’m still dealing with masses of mud at long distance. Can everyone please stop. I’ll clean up this thread when I get a moment. In the meantime, anyone who continues with this abuse will be permanently banned.

@Salient Green
Land use is big factor in the immediate run-off from a single deluge but once it’s been raining for days and the ground is saturated, local storage won’t do much. In this case, we had tens of centimetres of rain falling over a couple of days on already wet ground. It just wasn’t going to lie around on hillsides whatever the land use.

Then we will need to look at time for flow from Wivenhoe to Brisbane and all other events in Brisbane and Bremer catchments over that period.

Overall, I am still not sure that releasing the 50% plus gain in the period you claim it should have been released would not have caused any flooding in its own right. Basically, you are advocating for that period (unless I misunderstand) NOT using Wivenhoe for any flood mitigation storage. It would have been a brave and perhaps strange call to do that AT THAT TIME without any crystal ball knowledge of all rain events for the upcoming seven days.

This (www.nearmap.com) seems to be a good start for looking at the scale of the problem, with flooded areas like Graceville and St Lucia figuring prominently on the map. Colleagues in Graceville had finished renovations, which included raising parts of the house that were still inindated by about 15cm.

Revised planning instruments seem like a good start (minimise damage). Materials could be important too – it seems like a wall of hardwood planks would be less affected by inundation than a porous gyprock material? Also clearer insurance policies (to on-sell risks). Time will tell how much uninsured, underinsured, and coverage issues will emerge.

As for the human cost, can any mobile tower be directed to send out a warning SMS to all phones in the coverage area? Toowoomba is a very unlikely place to get flooded, being on top of the range with only two smallish creeks and a smallish catchment, and so normal warning systems radio/internet/tv etc seem to be unlikely to respond quick enough to freak flash flooding, while an SMS would get through to at least every second person directly, who will hopefully be in shouting distance of the other people.

Salient Green is attempting to both muddy the waters (sic) and split hairs to obscure the obvious. The BoM data that he quotes as taking place, for example, Maleny 10th 282mm, did not take place on Monday the 10th. It took place during the 24 hours prior to 9.00am on Monday 10th. That is, mostly on Sunday. Ditto for the day before.

It should also be noted that discharge rates can be seen to rise through a day without management input. There are a number of Flood Gates with a height of about 16 metres (don’t quote me) and their cross section increases as the water level increases, and their discharge rate increases accordingly. But this rise is in a limited range. Clearly, the number of gates needed to discharge 100 Gigs/day is about 1/6th the number required to discharge 650 Gigs.

So calls for hard evidence that no-one was actually at work on the weekend are standard ploys to obscure a conclusion by linking it to a barely relevant fact. What appears very obvious to most will be that the people with the authority to approve the opening of additional gates were either not at work, or were not contacted to enable them to make that decision.

The fact remains that an additional release of 100 Gigs/day over 3 days would have halved the subsequent panic release of 650 Gigs on Tuesday night/Wednesday morning. In fact, the 300 Gigs of extra buffer capacity would have allowed them the room to maintain a very modest 200 Gig/day flow right through the past week. It was an entirely avoidable flood.

Chris O’Neill, initially you questioned whether SEQ water staff were working on the weekend and now we know operators released 200,000 mega litres. Then you questioned whether the operators released enough water so as to minimise downstream damage. Well in todays news SEQWater Grid chief executive Barry Dennien insists that although the January 8-9 releases were relatively low compared with what occurred in the days afterwards, this was in accordance with the operating manual to mitigate flooding as nobody had foreseen the extreme rainfall that ensued. So don’t start a conspiracy.

@Ian Mott
Ian,Maleny telemetry reported 321mm to 9am on 10/1….and 135mm for the next 24hrs,and 196mm to 9am on the 12th.

Peachester 298,155,and 211mm for that 72 hours, Mt Glorious 203,262,and 230mm. Wivenhoe Dam picked up 500mm in the 48hrs till midnight of the 12th. These are hardly unimportant timings and volumes.

It was chucking it down all along the D’Aiguilar Range up until late evening Tuesday,as the 5.5m warnings were going out and Bligh and Newman were making public warnings.

A lot of rain fell after the weekend that SEQwater allegedly took off.

Streams entering Wivenhoe show two peaks,usually around midnight in Sunday 9th,and again midday to early evening on Tuesday 11th.

Throughout this period Wivenhoe increased discharges from over 100GL for the 24hrs to midnight 9th,140 or more on the 10th,at least 250GL on the 11th and culminating in 350GL or so on the 12th. All those figures are 24 hour volumes,the 645GL/day equivalent transient coming on that last day around midnight of the 11th. While discharges were increasing,so did storage,an indication of the magnitude of the floods,and of the mitigation function of Wivenhoe management plans.

As soon as that transient peak hits the river it starts to flatten out,so at no point downstream was a transient or sustained flow of anywhere near 645GL experienced,even with the addition of Lockyer Creek floodwaters.

You have absolutely no evidence that Wivenhoe was not monitored or managed on the weekend,when it is clear progressively increasing releases were made according to WaterGrid’s press release archive,and no evidence that the flood was ‘entirely avoidable’. Your statement that “discharge rates can be seen to rise throughout the day without management input” is an allegation.

Ian Mott, I have to question you on your expression “What appears very obvious to most..”

I have no knowledge of what ‘most’ may find ‘obvious’ but I do know that I have not been contacted so in this instance I do feel that I have been unfairly discriminated against. However, putting personal quibbles aside and reflecting on your methodology I now feel confident in saying that “What appears very obvious to most” is mostly to do with your observations and less about anybody else.

Lockyer Creek went to moderate flood level (12 m) just after 1 am on Friday morning and at this time the flow at Savages was just over half the flow at Rifle Range Road. The flow at Savages didn’t reach that flow rate (28 Gl/day at a level of 5.36 m which is below the minor flood level of 9 m) until 11 am so I guess it must take at least around 10 hours to get from Rifle Range to Savages. However, SEQ Water had let Wivenhoe go to 106.3% by 6 am Friday morning, even though Savages didn’t even get to minor flood level until after 10 am the next day. So the first question is: what were they doing on Thursday and Friday night that justified letting Wivenhoe get to 106.3% at 6 am on Friday morning?

The Lockyer then went back below moderate flood by 3 pm Friday and below minor flood by about 9.20 pm Saturday. Meanwhile, Savages was still only 5.63 m at 3 pm Friday and didn’t reach minor flood level until after 10 am Saturday. The second question is: why weren’t they releasing more water from Wivenhoe in this period? Wivenhoe would have been substantially higher than 106.3% and releases in this period would not have increased the flood peak in the Lockyer or have delayed its fall for very long.

The level at Savages did not reach moderate flood level (16 m) until 4 am Tuesday morning and included a period from 10 pm Saturday to 2 pm Sunday during which it started at 10.36 m and finished at 10.36 m. The third question is: what were they doing during this period? Is there some precious infrastructure below moderate flood level in the Brisbane valley that they were trying not to disturb? Hardly seems likely. If they had allowed a 16 m level at Savages for Saturday, Sunday and Monday, they could have released an extra 178, 146, and 74 Gl on those days respectively, a total of 398 Gl or 34% of Wivenhoe, and this doesn’t include doing anything different on Friday on the premise that it might have aggravated the Lockyer.

I agree with chris, if the dam operaters had operated with perfect hindsight, they would have the foresight to probably reduce the flooding.

And now seriously……

So far there appears to be no evidence that the dam was operated in any way except by the established protocol. With the important implication that the rainfall assumptions informing the protocols are inadequate. That this may berealted to AGW seems to be the conclusion is motivating some of the desperate attempts to play pin-the-blame-on-management that are popping up on the intertubes.

Hindsight is appropriate to review events and make adjusments, but not retrospectively blame others for failing to exercise hindsight in advance.

Chris O’Neill,you are suffering from an acute attack of hindsight. Operational policy was and is to lower the dam to 100% as soon as practical after a flood,not to go lower,no matter how beautiful the view is from here. 16m at Savages Crossing for three days does not mean that all damage downstream to Brisbane is avoided,and the big rain had not eventuated.Dynamical RF modelling is not very precise,particularly five days out.

The dam had been lowered back towards the regulation 100% from 123% on 29/12.they were at 102% on the 4/1,having shed about 250GL. This had caused flooding and bridge disruption downstream to Kholo Bridge. People use these bridges,and keeping them open is important day-to-day.

Around 1-6/1,rainfall was low or absent in the catchment,and stream level fell rapidly from the December freshs/minor flood in the catchment above Wivenhoe.

When rain returned on the 7 & 8/1,it was not particularly heavy,and inflows increased modestly,while discharges reflected this.The 9/1 saw very heavy rain return,and as the WaterGrid press releases attest,discharges increased incrementally. The dam level rose slowly at first,but they were discharging as well.

From then on saw very high rainfalls,which were notable for their bursts of extreme hourly intensity. If you review the stream data from the entire catchment, the graphs jump up and fall back often. The dam started to receive big influxes ,and was in mitigation mode,rising as it also increased discharges. It ain’t policy to immediately pass the flood,especially when they are not certain of whether the rain will persist.

The dam rose almost 70% between early am7/1 and early am11/1,around 800GL in volume. I estimate from Savages Xing data,subtracting estimates for the Lockyer[gauge malfunction] the dam discharged about 600GL in this time. That suggest inflows to the dam were around 1400GL for that period to early Tuesday 11/1.

River levels above the dam were falling between the pm10/1 and the am11/1,so it may have looked as though they were on top of it. But a new burst of very heavy rain sparked another peak,which is seen in the gauges peaking around midday or late afternoon. This jumped the dam by another 140GL to 191% or so later on 12/1,even as dam discharge was increased to its highest transient level of 7465 cusecs around midnight 11/1. Discharge seems to have been around 360Gl for the 24 hours to midnight 12/1.

Meanwhile,against forecast, the rain ceased very abruptly late on Tuesday 11/1 evening. That seems to make the higher releases perhaps avoidable but inflows stayed very high.

Yes,looking back,if only they had a crystal ball,and had pushed out 200 or 300 GL more over the 6-7-8/1,or 7-8-9/1….but it’s not like they did nothing. The strongly rising dam level was always tracked by increasing discharges. Psychic dam management is something for the future,however.

I estimate midnight 7/1 to midnight 12/1 discharges at around 950GL. Add this to level movements of about 80%/935GL,and you get around 1900GL inflow to the dam .

Since the peak,the dam has been drawn down according to policy from around 190 to 123% on the 17/1,a drop of 67%/780GL in five days. Downstream records sees The river flowing at 220-240GL for this period,subtract Lockyer water and you get maybe 1050GL in discharge.This means about 1350GL has entered the dam since the height of the floods. 7/1 to 17/1 inflows of around 3000GL.

These figures are approximate because of differing accounting periods,incomplete records,and because discharge at the spillway is faster than river flow at Savages Crossing

Chris O’Neill,you are suffering from an acute attack of hindsight. Operational policy was and is to lower the dam to 100% as soon as practical after a flood,not to go lower

Where did I say the dam should have been lowered to below 100%? I only ever suggested increasing releases when the dam was above 100%. It requires zero hindsight to stick to the following policy: allow the level to rise to just below moderate flood level at Savages whenever the dam is above 100%. If they don’t like it near moderate flood level when it’s only 100% then perhaps they could delay it to 110% but no more. What hindsight is required for that?

SEQ Water sounds like it has a bad case of serving two or more masters. Wivenhoe flood storage was not built to stop the bridges just below the dam from being flooded. Brisbane and Ipswich built and paid for the dam to prevent it from flooding them. If it wasn’t for Brisbane and Ipswich, there would be no Wivenhoe dam.

16m at Savages Crossing for three days does not mean that all damage downstream to Brisbane is avoided

This sounds like a case of “don’t mention the war”. As I said, Wivenhoe was not built to avoid flooding Fernvale and Mt Crosby bridges just downstream of it from minor (just below 16 m) floods. The enormous amount of money spent on Wivenhoe was not spent to save a few million making these bridges higher so they could avoid being flooded by a minor flood. You can’t serve two masters and that’s what SEQ Water were trying to do. Someone will tell them who their real master is but unfortunately that will be too late for this flood.

@Chris O’Neill
Chris, “…it requires zero hindsight to stick to the following policy..” Yep,a policy made in hindsight. Actually what they did was increase discharges throughout that period in the light of conditions on the ground. Forecast rain was heavy,but they still had not seen how truly intense rainfalls would become. 10-20mm/hr rates are moderate to heavy. They got rates of 30/50/100mm/hr over a lot of stations. Could they lead the trends,or could they only react to them? That’s not a rhetorical question.

Yes ,you did not personally suggest going below 100%. However,many other opinions I have read have done so. I apologise for including you .

Upping the rate of discharge at the dam wall is one thing,and it does make more room,but the water does not move down stream with equal alacrity. Potential developments in the tributary catchments cannot be factored out when judging releases.

The rain falls in the valley with the exception of the top end of the Stanley were not very high,in the 10 to 50mm range,and the “super-trough” of late 10th and the 11th and had not yet formed. Rain in the upper Brisbane got heavy a bit later. I’ve just watched a radar replay for the period,and the wind directions and rainfall distribution is quite changeable and spotty. Volatile conditions without persistent trends for a while when it probably counted most for an aggressive anticipatory release.

Are you sure that persistent moderate flood levels down to the Bremer are only damaging to bridges? Whatever,I kind of think that for a while they thought the unfolding rainfalls and flows were not leading anywhere as dramatic as it became,and that minimising downstream flooding was a realistic outcome. I don’t think in real time, future developments were as clear cut as they became and as inevitably they are now seen.

“Brisbane and Ipswich paid for the dam to prevent it from flooding them” Really? Must be another dam you’re talking about,because the dam they got was never going to prevent another 1974,just mitigate it. That was made clear at the time,and is reflected in a good deal of public information…maybe not enough. It does a good prevention job on minor to moderate floods.

“If it wasn’t for Brisbane and Ipswich there would be no Wivenhoe Dam” If it wasn’t for Wivenhoe there would have been a whole lot less of Brisbane right now,and we’d be a bit short for water most of the time.

The dam is absolutely critical for water supply.It must be raised,because its yield is largely committed,and this flood has tested its limits.

“…it requires zero hindsight to stick to the following policy..” Yep,a policy made in hindsight.

Why didn’t they have that policy to begin with? I’ve already explained why they should have had that policy to begin with.

Actually what they did was increase discharges

very slowly

throughout that period in the light of conditions on the ground. Forecast rain was heavy,but they still had not seen how truly intense rainfalls would become.

So they’re supposed to assume the weather forecast is going to be very accurate? Sounds like a foolish assumption to me.

Potential developments in the tributary catchments cannot be factored out when judging releases.

As I said, Lockyer creek went back below moderate flood level by 3 pm Friday the 7th. Additional releases from then (when Wivenhoe was already more than 106.3% and rising) did not need to cause The Lockyer to go back above moderate flood level. Why weren’t they releasing more then?

Are you sure that persistent moderate flood levels down to the Bremer are only damaging to bridges?

I didn’t say “moderate” flood levels. I said “just below moderate” flood levels, i.e. a minor flood. And I didn’t say they were damaging to bridges. They just get flooded. And as I said, Wivenhoe was not built and paid for to prevent minor floods in the part of the river downstream to the Bremer junction. Anyone who thinks there should be no minor floods in that part of the river is just foolish.

I kind of think that for a while they thought

assumed

the unfolding rainfalls and flows were not leading anywhere as dramatic as it became

“Brisbane and Ipswich paid for the dam to prevent it from flooding them” Really? Must be another dam you’re talking about,because the dam they got was never going to prevent another 1974,just mitigate it.

I can see you like playing with words. I’ll try to be clearer:

Brisbane and Ipswich paid for the dam to mitigate flooding in Brisbane and Ipswich, not to prevent minor flooding in the Brisbane Valley down to the Bremer junction.

It does a good prevention job on minor to moderate floods.

In that case it hardly seems worth having it. The damage avoided by avoiding minor floods in the Brisbane valley down to the Bremer junction is just totally insignificant compared with either the cost of Wivenhoe dam or the cost of the flooding in Brisbane. Even if there was only a one in a thousand chance of the rainfall on Sunday, Monday and Tuesday, I expect the risk-weighted cost of the flood damage in Brisbane is far more than the cost of damage in the middle Brisbane valley from a minor flood.

“If it wasn’t for Brisbane and Ipswich there would be no Wivenhoe Dam” If it wasn’t for Wivenhoe there would have been a whole lot less of Brisbane right now,and we’d be a bit short for water most of the time.

Thanks for the non-sequitur. Since you like to use my quote out of context, I’d like to put some context back in. The enormous amount of money spent on Wivenhoe was not spent to save the middle Brisbane valley from minor floods. You can’t serve two masters and that’s what SEQ Water were trying to do. Someone will tell them who their real master is but unfortunately that will be too late for this flood.

Now the big issue starts to emerge. Our uninsured businesses are playing for a bailout from the public purse. ‘Donations’, ‘donations’, they cry.

I would expect that if entrepreneurs want to supposedly add a cost impost onto commodities (to pay for their skill!?), that this should include monitoring objective issues – such as flood plains and insurance coverage.

However, presumably by skimping on insurance and locating on cheap plots of land, these businesses – with bad business practice – thereby obtain an artificial, unfair competitive advantage compared to their competitors who locate on preferred flood-proof sites or pay for flood insurance.

The risk of 50 year floods is not expensive to insure against. You just need to cover 2% of rebuilding and contents costs – after depreciation. There is no sense in allowing development on sites with greater flood risk, but presumably the cost of insuring against a 100% loss every 25 years would not be enormous.

All this means that, as our climate is changing, the State must provide insurance services. This is the only way the costs of events such as the Queensland and Victorian floods and bushfires etc, can be spread over a wide enough insurance base.

If working people were only able to live on a flood plain because of high rents then this also indicates that the State must step in to provide affordable accommodation in safe areas.

So maybe the floods have some good – they wash away bad businesses, bad housing, and bad insurance companies.

Chris,you have to know this. Wivenhoe was predicted to knock a 1974 flood down by perhaps two meters in Brisbane city. This was based on modelling of that flood . That means 1974 would still have made major flood level at 3.5m. While clearly 3.5 is better than 5.45 it is still destructive. We now have had a flood of similar peak intensity or more,while not the duration of 1974,according to one of the experts,and we get to 4.6. Not good but better 5.45,and better than 6. Every ten centimetres,maybe centimetre counts,as bitter a sop that must seem to many. My brother’s neighbour in West End had water reach within a centimetre of her floorboards.

Wivenhoe can’t serve two masters? What are the options? It has to and will sometimes do inadequate jobs for both. Sometimes we need to recognise when an inadequate job is the best possible in the circumstances. We can explore the consequences for Ipswich of running a high Brisbane River.

Flooding there is a delicate balancing matter,running the river too high will back a minor flood up to Ipswich. In fact you can see today that,now that releases have been eased back to just on moderate flood at Mt Crosby,water is finally beginning to drop below 8m, a metre above minor flood level. Had Bremer/Warrill flows been at all elevated from their own basin’s runoff, the high releases of the last few days would not have been safe. One of the dividends of cutting discharges today has been to drop the last of the flood out of Ipswich in the face of the forecast storms which started up yesterday, and have been quite severe enough today. It looks like the lowering of the dam has been achieved just in time. They are still sticking to the manual,though.

Pushing the dam discharge up to make your suggested 16m at Savage’s would have backed significant water up the Bremer because it was flooding from its own catchment over 8th to 10th at the time,as the traces for Purga Creek, Warrill Creek and the Bremer @Walloon show. This would have genuinely made trouble in town. This is probably why the Bremer and Lockyer situations are mentioned in the morning press release from WaterGrid on the 10th. The significance of backing up the Lockyer I don’t know,but why note it in the press release if it wasn’t a concern at those not insubstantial heights.

You seem convinced that water managers opened up the gates too slowly. I’m simply not convinced for a few reasons. We do not have the hourly rainfall data the managers tracked in real time, so we can’t see it the way they did. I’m not sure that the downstream concerns can be dismissed easily and the gains would be significant for Brisbane town. Has your adjustment won 400 GL over the three days at the expense of parts of Ipswich? Maybe 200 was available with prudence,300? If the lower figures are more realistic,how much would 15-20% extra flood capacity have lowered the peak? If the serendipitous cessation of rain at 11pm 12/1 had not come? If strong onshore winds were pushing the river back up from Moreton Bay.

It does a good prevention job on minor to moderate floods-very much worthwhile- and it mitigates major floods in most scenarios,in a way that is not always what we might hope. Live with it.

If you’ve got a figure you’re confident in for a lower height at the City gauge,show me.

Nick provided a cogent and convincing argument backed with facts and figures. Chris O’Neill replied with the same oft-repeated assertions, emotional thinking and specious arguments which rely on 20/20 hindsight.

There is no point in debating with people who are wholly unreceptive to logic.

Meanwhile, back at 6 am on the 7th, Wivenhoe was at 106.3%. However, on the 7th, the flow rate didn’t rise above 46 Gl/day and averaged 28 Gl/day over the whole day.

Is there any explanation why, even though the dam level is about the same, they were releasing water much, much faster today than they were on the 7th? It couldn’t possibly have anything to do with what happened since then because as we all know, they operate “by the book”.

I said he was wholly unreceptive to logic. He said I was blind. In the context, these statements are functionally equivalent as “abuse”.

If Chris O has suffered flood damage then I am sorry for him. However, he has been making assertions of serious professional incomptence at a fairly small and easily identifiable group with reasoning that is very debateable. Why is this OK? Yet when he is taken to task he is protected. This seems odd.

I don’t care who hit who first. Chris O’Neill, you should have taken my warning to Ikonoklast as being meant for you also. Also, I may be oversensitive, but I don’t like the use of “blind” as a pejorative.

I request that both of you stop commenting in this thread, and that everyone else behave themselves.

Wivenhoe was predicted to knock a 1974 flood down by perhaps two meters in Brisbane city. This was based on modelling of that flood. That means 1974 would still have made major flood level at 3.5m. While clearly 3.5 is better than 5.45 it is still destructive.

It’s vastly better than 5.45 and still enormously better than 4.46. The major flood level is 3.5. That description should mean something significant. For example, it should determine planning policy. Indeed, going by the ABC reports, not many homes were flooded until it got close to major flood level.

We can explore the consequences for Ipswich of running a high Brisbane River.

You appear to have accepted that direct effects of minor flooding in the middle Brisbane valley is a relatively insignificant issue. Hopefully I’m making progress.

Pushing the dam discharge up to make your suggested 16m at Savage’s would have backed significant water up the Bremer because it was flooding from its own catchment over 8th to 10th at the time,as the traces for Purga Creek, Warrill Creek and the Bremer @Walloon show.

No, that’s not true. None of those had a lot of flow on Saturday and Sunday, there wasn’t much total flow on Friday and there wasn’t a real lot on Monday either. So releasing a minor flood down the middle Brisbane on Saturday and Sunday and I guess Friday would only have produced a minor flood a relatively short distance up the Bremer from the junction. They could have kept the release going after midnight on Sunday and cut it back during the day if they were worried about the Bremer but judging by events I very much doubt they would have cut it back to save the Bremer until Tuesday.

You seem convinced that water managers opened up the gates too slowly. I’m simply not convinced for a few reasons. We do not have the hourly rainfall data the managers tracked in real time, so we can’t see it the way they did.

So you’re claiming there’s no evidence either way. They certainly didn’t increase it enough on Friday when the dam was already too high. 67 Gl came down the Brisbane River on Friday at Gregors Ck alone without including the amount that came from Somerset dam. They only let 28 Gl get to Savages on Friday including the amount that came from the Lockyer. 71 Gl came down past Gregors excluding Somerset on Saturday and only 89 Gl including 14 Gl from Lockyer went past Savages. This all happened when the dam was already clearly too high and rising. If that’s not acting too slowly I don’t know what is.

Has your adjustment won 400 GL over the three days at the expense of parts of Ipswich?

I don’t think so for the reasons I described above. The Bremer was OK until Tuesday. And there was potentially another 240 Gl on Friday as well but probably less than this because it might have reduced the dam back to 100% before this much was released. Perhaps another 100 Gl extra could have been released if Friday was used.

If the serendipitous cessation of rain at 11pm 12/1 had not come?

If heavy rain had continued indefinitely then sooner or later there will be flooding. My point is their policy has to be based on allowing some sensible level of flood below the dam to preserve the flood reserve. The levels they had on Friday and Saturday morning were clearly too low and considering the value of the asset they were meant to protect the level was still too low the rest of Saturday and Sunday. Even on Monday morning, because the flood reserve by then was hugely compromised, they still didn’t allow enough flow considering the big increase in risk they were then taking.

They could have kept savages to a minor flood level on Saturday, Sunday, Monday, Tuesday and Wednesday and released 5 days X 267 Gl/day = 1335 Gl past Savages which is more than the total they actually released past Savages over those 5 days of 1274 Gl. The difference of course, is that one would have produced just a minor flood while the other produced a major flood that peaked more than 3 metres higher than the major flood level. There’s 59 Gl to spare in that and I guess another 100 Gl could have been released on Friday. I think the total going down the Bremer on Tuesday and Wednesday was around 200 Gl, so I guess using the spare 59 Gl and 100 Gl from Friday might have been enough to mitigate the Bremer. There wouldn’t be much left over to take it above the moderate flood level at Savages.

If you’ve got a figure you’re confident in for a lower height at the City gauge,show me.

I would expect that the same flood levels, minor, moderate and major should have some comparability at different gauges on the same river. So if it gets to moderate flood level at one gauge then it shouldn’t get too far off moderate flood level at other gauges further down the river. Thus if you had a flood right at the beginning of the moderate level at Savages I would expect it to be very difficult to get up to major flood level at gauges lower down the river, and not quite as difficult but still difficult where the river is tidal.

@Chris O’Neill
Chris,I stand by my reconstruction of events re flooding in Ipswich. Your higher release would have backed up the Bremer,which was flooding,though yet to reach the higher levels of 24 to 48 hours later. Ipswich flooding begins at rather low levels. I reckon you do have a hypothetical gain but not as much as you think.

Flood stages at different gauges cannot be related to others easily. Flood levels in individual areas are based on the river and flood plain profiles,as well as water level relationships to significant structures like bridges and weirs.

This inquiry will produce some interesting and painful observations,but I think more to do with land use decisions post dam. No doubt someone can find the Trevor Grigg/Co-Ordinator General’s Department study from 1977 “Comprehensive Evaluation of the proposed Wivenhoe Dam”.

Is my week up yet? I cant remember. I think Chris Oneill is asking some reasonable questions regarding the weekend in question and why was the Wivenhow dam was allowed to fill to a level well above normal. Its the weekend activities that concern me, given the dam has been privatised. Not an unreasonable question.